Radio frequency communication over large or wide geographical areas has posed significant problems in the past Systems of this type generally must make communication available for radio units which have low power transmitters and which can move in any direction within the wide area coverage. Although there exist a number of systems of this type, few systems have been designed to cover generally inaccessible areas, or frequency blocked areas. For example, a subterraneous location such as a subway is inaccessible to wide area coverage systems operating above ground, because their transceivers cannot overcome the blocking effect of the earth.
Most systems which have been designed to address frequency blocked areas use multiple low power repeaters which are spaced at designated points to avoid the frequency blocking obstruction. Unfortunately, the use of low power repeaters is expensive to implement and burdensome to maintain.
There have been attempts to cover frequency blocked areas using radiating coaxial cables, as an antenna, to distribute the communication channel throughout the intended coverage area. Systems using this approach, however, have been limited to relatively small coverage areas due to the inherent signal loss in such coaxial cable. Moreover, these systems have failed to provide effective system management capability; for example, monitoring and controlling the system to handle: faults, system reconfigurations and on-going adjustments such as tuning and power level adjustments.
In most wide area coverage systems, such system management is accomplished by transmitting control and status response commands from a central computer to the respective repeaters. Because each repeater is in direct communication with the central computer, transmitting commands and/or receiving status information from the repeaters and other remote devices does not pose a significant problem.
Unlike many wide area coverage systems, systems designed to cover frequency blocked areas cannot communicate directly with a central computer. A central computer in a system covering frequency blocked areas is, by definition, blocked from communication with each of the repeaters or other remote system components.
Known prior art systems designed to provide communication in frequency blocked areas have been unable to provide control and monitoring functions with respect to the various components in such systems in a reliable, efficient and cost-effective manner.